Feedstock clamping means

ABSTRACT

IN A CLAMPING ARRANGEMENT FOR CLAMPING A FEEDSTOCK BILLET EXTENDING INTO A HIGH PRESSURE CHAMBER AGAINST AXIAL FORCES WHICH ACT ALONG THE LENGTH OF THE BILLET AND ARE SUFFICIENTLY LARGE TO DEVELOP STRESSES GREATER THAN THE YIELD STRESS OF THE BILLET MATERIAL, A PORTION OF THE FEEDSTOCK BILLET IS CLAMPED BETWEEN CLAMPING MEMBERS. THE CLAMPING MEMBERS ARE SEPARATED FROM THE INTERIOR OF THE HIGH PRESSURE CONTAINER BY A PASSAGE CAPABLE OF PASSING THE BILLET WHEN THE CHAMBER IS NOT UNDER PRESSURE. WHEN THE PRESSURE IN THE CHAMBER IS HIGH, RELATIVE DEFORMATION OCCURS BETWEEN THE PASSAGE WALL   AND THE BILLET TO PROVIDE FRICTIONAL ENGAGEMENT OVER A LENGTH SUFFICIENT TO REDUCE THE STRESS IN THE BILET TO A VALUE BELOW ITS YIELD STRENGTH IN THE REGION ADJACENT THE CLAMPING MEMBERS.

United States Patent Y 3,415,088 12/1968 Alexanderetal "basal;

Inventors John Malcolm Alexander;

Ieh Leqyel; Peter Gay Aahlord, London,

FEEDSTOCK CLAMPING MEANS 6 Cid-a, l4 Drawhg I'lga.

us.c| 12/, 12/110, 12/210 int. (1 am 22/10 musmu...- 12/253, 210, 211.S6, 60

lehreaeea Clad UNITED STATES PATENTS Primary Examiner-Charles W. LanhamAssistant Examiner-A. L. Havis Attorney-Larson, Taylor, 8; HindsABSTRACT: In a clamping arrangement for clamping a feedstock billetextending into a high pressure chamber against axial forces which actalong the length of the billet and are sufficiently large to developstresses greater than the yield atreu of the billet material, a portionof the t'eedatoclt billet is clamped between clamping nmbers. Theclamping member: are separated from the interior of the high pressurecontainer by a pauage capable of passing the billet when the chamber isnot under pressure. When the preaaure in the chamber is high, relativedeformation occurs between the paaaage wall andthe billet to providefrictional engagement over a lengthaufficicnt to reduce the street inthe billet to a value below its yield ttrength in the region adjacentthe clamping members.

PATENTEU JUN28 1971 sum 2 OF 4 FEEDS TOCK CLAMPING MEANS The presentinvention relates to clamping means for clamping feedstock billetsagainst axial forces acting along the length of the billets andsufficiently large to develop stresses greater than the yield stress ofthe billet material. Such clamping means are required for example in thecyclic hydrostatic extrusion of billets. Each cycle of such an extrusionprocess comprises the .stepsof advancing the continuousbillet into achamber, clamping the billet, applying a very high pressure to theinterior of the chamber a portion of the billet is extruded through anextrusion die and thereafter reducing or removing the pressure to enablethe billet to be once more advanced into the chamber, the extrusionproducedremaining in one piece with the billet.

The cyclic hydrostatic extrusion process requires means for clamping alength of billet or feedstock in a region where it passes through a wallof a container capable of withstanding a high hydrostatic pressure. Inthe course of a cycle of cyclic hydrostatic extrusion, the clampingmeans must be capable of securely holding the feedstock billetagainst alarge end force exerted on it from within the container and thereaftermust be easily freed to enable a length of the feedstock billet to passthrough the clamping means into the container. Moreover itis desirablethat the clamping means should be capable of accommodating acomparatively large tolerance range of feedstock billet tolerances sothat the apparatus may be used for cyclic extrusion of hot-rolled orcast billets. It is further desired that the feedstock billet' shouldnot be appreciably marked as the result of the clamping operation.

In accordance with this aspect of the present invention, there isprovided a clamping means for a feedstock billet to hold the billetagainst a large end force, the said clamping means comprising arigid-walled passage permitting the passage therethrough of feedstockbillet up to the maximum required tolerance limit, and means forreleasably'holding the billet at the back end of the passage, that'is-at the end'remote from the force, while the billet deforms intofrictional contact with the passage wall.

When such clamping means are usedin cyclic hydrostatic extrusion,increasingly high hydrostatic pressure'within'the container deforms thebillet into frictional contact with the wall of the passage. The greaterthe pressure within the container, the greater will be the end forcetending to deform the billet, and hence the greater will be thefrictional contact between the billet and the wall of the passage.

The deformation of thefeedstock billet in the passage is in generalcaused by buckling and upsetting. This occurs preferentially at theforwardend of the passage so that-the force applied to the holding meansat therear end of the passage does not appreciably exceed the yieldstress of the feedstock billet material.

When the pressure in the container is reduced, the deformed portion ofthe feedstockbillet will usually have sufficient resilience to freeitself from the wall of the passage :so that a further-lengthoffeedstock-billet may be fed into the container without binding. However,in order to facilitate this operation, it is preferred to form thepassage by means of clamping passage members, also referred tohereinafter as a sizing-tube, the interior of which has the requiredcross section to form the said passage, the sizing-tube being formed ofa number of segments which can be moved outwards away from the axis ofthe passage to free the feedstock billet. The'sizingtube segments may beforced together to define the passage by mechanical or hydraulic means.Where the surface of the billet is-deflned by a number of planes, thesizing-tube maybe divided along these planes so that each segmentmayslide relative to its neighbor into contact with thebillet withoutaffecting the movement of the neighboring segment. This is particularlyadvantageous where the feedstock billet is in the form of a cast ingot,such ingots tending to vary considerably in their cross-sectionaldimensions. In some cases thecontact between the deformed feedstockbillet and the wall of the sizing-tube could beso complete around theforward end of the sizingtube as to avoid the need for any additionalseal to prevent the escape of fluid under pressure from the container.

The shape of the exterior of the sizing-tube may be cylindrical ortapered or any other desired circular or noncircular shape.

In accordance with a further aspect of the present invention there isprovided a clamping means for a feedstock billet passing through a wallof a high pressure container, the said clamping. means comprising adeformable-walled passage which in its relaxed state permits the passageof billet material therethrough, the rear end of the passage beingsupported while the front end of the passage is subjected to the fluidpressure in the container, the arrangement being such that the containerpressure deforms the passage wall into gripping contact with thefeedstock billet. Sueh an arrangement is particularly advantageous wherethe feedstock billet material is brittle. It may also avoid the need fora seal to prevent the escape of fluid from the container between thefeedstock billet and the passage wall.

Embodiments of these and other aspects of the presentinvention and theirapplication to cyclic hydrostatic extrusion apparatus will now bedescribed by way of example with reference to the accom'panyingdrawings,in which:

FIG; 1 shows in side elevation at length of feedstock billet which hasbeen clamped between three clamping jaws, the right hand'end ofthe'feedstock billet having-been subjected to high hydrostatic pressure,

FIG. 2 shows one form of clamping means in axial section,

FIG. 3 is a view similar to FIG. 2 of an experiment to determine thebehavior of an unsupported length between the sizing-tubeand the holdingmeans.

FIG. 4a through 4h show in cross section a number of arrangementsforming the sizingtube segments,

FIG. 5 is a longitudinal sectional view of an alternative clampingarrangement employing a resiliently deformable sizing-tube, thesizing-tube being shown in its relaxed state,

FIG. 6 is a view corresponding to FIG. 5 showing the clampingarrangement in operation under high pressure, and

FIG. 7 is'an axialsection of another embodiment of the feedstockclampingmeans of the present invention.

The length of feedstock billet shown in FIG. 1 has been clamped betweenthree clamping jaws in the form of segments which'together make up acomplete cylinder extending over a length 1 The right hand end of thespecimen was then subjected to a-high hydrostatic pressure in-excess ofthe yield stress of the material of the specimen, in this casecommercially-pure aluminum. This caused the material to deform intoclose contact with the surfaces of the clamping members and inparticular resulted in the formation of flashes 2 on the surface ofthe-specimen l where the billet material was forced into the crevicesbetween adjacent clamping members. It will be noted thatthe flashes2-are of greatest height at the right hand end of the clamped portion'and extend altogether over a length =1 which is appreciably less thanthe total clamp length 1 From this it is deduced-that the deformation ofthe billet material is greatest at the right hand end, that is at theend nearest the high hydrostatic pressure, and that the deformationdiminishes progressively with distance away from this region until aregion 3 is reached wherethere is no deformation of the material. Thisindicates that to the left of the region 3, the clamped portion oflength l ---l is subjected to an end pressure less than the yield stressof the material.

In order to prevent marking of the feedstock billet by the clampingmeans, it is apparent that in the region 1 the clamping means mustpresent the desired smooth continuous support surface against which thebillet material can be deformed. In the region *1, to the left of theregion 3, the necessary clamping pressure does not exceed the yieldstress so that the feedstock billet can be adequately held here withoutmarking it.

FIG. 2 shows an embodiment of clamping means based on this hypothesis.In the arrangement shown in FIG. 2, a length of feedstock billet l isclamped by means of a set of jaws 4 similar to those which had been usedon the specimen shown in FIG. 1, the clamping pressure of the billetbeing however less than the yield stress of the billet'rnaterial. Theright hand end of the billet 1 passes through an opening 5 in a highpressure container 6 in which a high hydrostatic pressure greater thanthe yield stress of the billet material can be generated. A sizing-tube7 of length 1 has a cylindrical bore 8 in which the billet 1 is a loosefit. A high pressure fluid seal 9 is located in a recess in the frontend of the sizing-tube 7 adjacent the wall of the container 6. Thecombined length of the clamp formed by the members 4 and the sizing tube7 is 1 corresponding to the required total length 1, in the specimen asshown in FIG. 1 to provide the necessary frictional force to hold thefeedstock billet.

In operation, the clamping means 4 are applied against the feedstockbillet and the pressure inside the container 6 is then progressivelyraised. When this pressure reaches the yield stress of the billetmaterial, the latter begins to deform initially in the region of theseal 9 to contact the wall of the bore 8. As the contact between thebillet material of the bore wall is inevitably frictional, an additionalfrictional holding force will be available to resist movement of thefeedstock billet I. As the pressure in the container rises further, theregion of deformation of the billet material will extend progressivelyto the left of the seal 9. Since the spread of deformation of thematerial requires movement of the material nearer to the seal 9, it isobvious that the stresses and also the sizing-tube/billet interfacepressure will be greatest adjacent the seal and will steadily diminishwith increasing distance to the left of the seal 9. By appropriatechoice of the length 1, in relation to the maximum pressure in thecontainer 6, the radial compressive stress at the rear or left hand endof the sizing-tube 8 may be equal to or even less than the yield stressof the billet material even when the pressure within the container isconsiderably greater than the yield stress. Consequently the holdingmeans 4 do not needto exert a pressure on the feedstock billet which isgreater than the yield stress of the billet material so that appreciablemarking by the jaws 4 or by extrusion between the jaws 4 is unnecessary.

FIG. 3 shows an experiment conducted to confirm the operation of theclamping means shown in FIG. 2. In this experiment, a length offeedstock billet I1 is mounted in a 6-inch long hardened steel tube 12having a /16-inch reamed bore, the tube 12 being tapered on the outsideand split into two halves along an axial plane. The two halves are heldtogether by forcing an outer sleeve 13 having a correspondingly taperedbore over the tube 12 with a substantial preload which ensures that nogap can occur at the interface between the two tube halves when a radialpressure of 40 tons per inch square acts in the bore. The billet 11 wasof commercially pure aluminum and was able to slide freely in the borebefore pressure was applied. A Ila-inch projection 14 at the rear end ofthe tube 12 was enclosed in a spacer 15, the bore in the spacer beingrelieved to ls-inch diameter for most of its length to provide aclearance 16 between it and the billet l l. The back endface of thebillet 11 was abutted against a stop-bar 17 secured by tie rods 18 to ahigh pressure container 19 into which the forward end of the billet 11projected through a seal 20.

Tests were carried out with a number of billets. First a billet with aninitial diametral clearance of only 0.0005 inch was placed into the tubeand pressure applied in increments of 5 tons/in up to 40 tons/in. Aftereach pressure application the specimen was examined and it was foundthat, at the maximum pressure, the diameter of the unsupported part 14of the billet increased to a size 0.002 inch larger than the bore of thesizing tube. In one test, after reaching the 25 tons/in stage, thecontainer was depressurized and a thin washer was inserted into theendstop assembly, to provide a 0.03-inch air space at the end of thebillet. On the reapplication of pressure the billet retracted smoothlyuntil the end stop was contacted once more, indicating the continuedneed for some slight axial restraint. The unsupported length 14 of thespecimen slightly buckled when the initial clearance was increased to0.004 inch and the unsupported diameter increased as before to a size0.002 inch above the sizing-tube diameter. These experiments indicatethat, if the holding means is closely adjacent to the sizing tube, fullcontrol of the feedstock is possible without clamping marks of anyimportance remaining on the billet surface.

In order to facilitate the release of the billet from the sizingtubeafter release of the end force, for example on depressurizing of thehydrostatic pressure container, it is desirable that the sizing-tubeshould be split into two or more segments as in the case of thesizing-tube 12 shown in FIG. 3. FIGS. 4a to 4h show in cross section anumber of possible arrangements of the sizing-tube segments. In FIG. 4a,the billet l is of circular section and the sizing-tube is divided intothree equal segments. FIGS. 4b to 4d show three alternative methods ofholding a square section billet, the sizing-tube being divided intosegments by planes coincident with the boundary planes of the billet.FIG. 4e shows a modification of FIG. 4d for use with a square sectionbillet having rounded edges. FIGS. 4f to 4h show arrangements for thesizing-tube segments for use in holding billets of other cross sections,the planes of division between the sizing-tube segments coinciding withthe plane surfaces of the billet.

When individual straight bars of feedstock are loaded in succession intothe machine, the function of the sizing-tube will permit the abuttingend-faces of adjacent billets to be unprepared in respect of flatnessand squareness. Badly matched end-faces will be fully merged as thejoint passes through the compression zone of the sizing-tube.

In view of the comparatively small holding force required to be appliedby the holding means, it may be sufficient in some cases for thesizing-tube additionally to perform the function of the holding means.For this purpose the arrangement shown in FIGS. 4d to 4g are appropriatesince each sizing-tube segment can be applied by a force in thedirection of the arrow shown without interfering with the propermovement of its neighbors. Such arrangements also enable the separateseal to be dispensed with. Moreover the independent movement of eachsegment enables the sizing-tube to accommodate the full range oftolerances for the billet.

The sizing-tube segments may be actuated by the pressure within thecontainer or by other externally operated means.

The arrangement shown in FIGS. 5 and 6 comprises a high pressurecontainer 21 having an inlet opening 22 for the feedstock billet 23.Mounted in the container 21 adjacent the opening 22 is a resilientlydeformable sizing-tube 24 which in the relaxed state may have the shapeshown in FIG. 5.

External holding means 25 hold the billet 23 against the initial endforce which may be exerted on the billet 23 as the pressure within thecontainer 21 begins to rise. As this occurs, the sizing-tube 24 isdeformed into sealing contact with the billet 23. The rising fluidpressure causes axial compression with the sizing-tube starting from theright hand end, that is the end in contact with the fluid. This causes aradial pressure inwards against the billet to oppose radial extension ofthe billet and to grip the latter frictionally. As the containerpressure rises, a pressure gradient is set up along the feedstocksurface. Even when the full pressure within the container is reached,for example a pressure sufficient to cause extrusion of the billetthrough a die (not shown) the pressure gradient along the feedstocksurface diminishes from the full container pressure at the right handend to a value below the billet material yield stress in the region ofthe opening 22.

If desired, the sizing-tube 24 may in its relaxed state have the shapeshown in FIG. 6, passage of the billet 23 through it being effected byallowing the tube 24 to deform to the shape shown in FIG. 5 as a resultof frictional contact between the moving billet and the tube. 1

The resilient sizing-tube may be of corriposite construction of morethan one material for example it may be laminated and it may have aconical or other noncylindrical outer shape. The resilient material mayinclude suitable rigid reinforcements and may be loaded with suitablefilling materials to obtain the characteristics required to suit thebillet material.

FIG. 7 shows in axial section another embodiment of feedstock clampingmeans employing a segmented rigid sizingtube 31. The sizing-tube has acylindrical external surface around which snugly flts a rubber sleeve32. Pressure is applied around the outside of the sleeve 32, thispressure for example being that generated within the high pressurecontainer, and this pressure holds the segments of the sizing-tube inthe closed position.

The holding means comprise a set of clamping jaws 33 which are appliedagainst the feedstock billet 34 by force of diametrically opposedplungers 35 operated by any convenient source of fluid pressure.

We claim:

1. Clamping means for clamping a feedstock billet against forces appliedto said billet in the axial direction thereof by high pressure in achamber, said chamber having an opening through which said billet canextend, said clamping means comprising: clamping members including meansfor gripping said billet with a pressure sufficient to frictionallyclamp the billet but insufficient to substantially mark said billet;clamping passage members together defining a clamping passage throughwhich said billet is slidable, said clamping passage members beingseparable to increase the effective cross-sectional area of saidpassage; means for forcibly holding said clamping passage memberstogether and sealing means separating said clamping passage from saidchamber opening,

said sealing means being arranged to seal against said billet to preventfluid from said chamber entering said clamping passage; said clampingpassage having a length sufficient to reduce the stress in the billet toa value below its yield strength in the region of the billet adjacentthe gripping members.

2. Clamping means according to claim 1, in which said clamping passagemembers are bounded by axial planes of separation between adjustingclamping passage members.

3. Clamping means according to claim 1, in which a flexible tubesurrounds said clamping passage members and means are provided forapplying fluid pressure from said chamber around said flexible tube.

4. Clamping means according to claim 1, in which said clamping passagemembers are bounded by axial planes of separation between adjacentclamping passage members in which a flexible tube surrounds saidclamping passage members and means are provided for applying around saidflexible tube the fluid pressure in said chamber.

5. Clamping means according to claim 1, in which said clamping passagemembers are segments ofa sizing tube, the external surface of saidsizing tube being a surface of revolutron.

6. Clamping means according to claim 5, in which said external surfaceof said sizing tube is tapered to cooperate with a correspondinginternally tapered sleeve.

